Collaborative Research: Genetic diversity, resistance genes, and negative density dependence in tropical tree seedling dynamics

热带森林以其高度的多样性和大量的稀有物种而闻名。 最近的研究发现，与常见物种相比，稀有热带树种遭受的病原体专属于单一宿主物种，然后通过该单一宿主的密集幼苗迅速传播。 这项研究将测试一个新的假设，即稀有物种受到宿主特异性病原体的影响更大，因为它们在种群水平上具有较低的抗性基因多样性，因此它们所有的幼苗都对同一套病原体敏感，促进病原体快速传播并增加死亡率。 这一假设将测试实验温室和实地研究，结合遗传分析，将量化的多样性抗性基因的稀有和常见的树种在低地热带森林的巴罗科罗拉多岛，巴拿马。计算机模拟还将用于研究抗性基因多样性的测量差异是否会影响感染水平，死亡率和当地树种的丰富度。这项研究的结果将提高对植物-病原体相互作用的理解，并具有农业和园艺的潜在应用（例如提高作物的病原体抗性）。将通过为学生和教职员工举办的夏季讲习班向更广泛的受众提供尖端遗传技术的实践培训，这项研究将是第一次从树木社区获得大型转录组数据集，并将提供基因序列数据，为今后研究热带森林的遗传多样性提供信息。抗性基因多样性对森林动态的影响的研究将弥合分子进化研究之间的差距，表明在许多位点正在进行的多抗性基因的选择，以及这种多样性在自然界中如何发挥作用。此外，这项研究很可能弥合热带植物多样性的竞争理论，提供了一个遗传解释，为什么稀有树种更强烈地控制他们的物种特异性的敌人，同时支持扩散限制作为一个功能，确定哪些物种是当地占主导地位。最终，这项研究应该阐明当地稀有性是否限制了当地的遗传多样性，这反过来又加强了当地的稀有性，只有通过长距离花粉或种子移动招募新的等位基因才能逃脱这种循环。证明种群的生态和遗传特征之间的这种耦合将为进化和生态学的理论进步带来新的视角和途径。该项目将为本科生和研究生以及博士后研究人员提供研究经验。

Tropical forests are famous for their high diversity, as well as the large number of rare species they harbor. Recent studies have found that, compared to common species, rare tropical tree species suffer more from pathogens that are specialized to a single host species that then spread rapidly through dense patches of seedlings of that single host. This research will test the novel hypothesis that rare species are more strongly impacted by host-specific pathogens because they have lower diversity of resistance genes at the population level, such that all their seedlings will be susceptible to the same suite of pathogens, promoting rapid pathogen spread and increasing mortality rates. This hypothesis will be tested using experimental greenhouse and field studies, combined with genetic analyses that will quantify the diversity of resistance genes for rare and common tree species in lowland tropical forest on Barro Colorado Island, Panama. Computer simulations will also be used to examine whether the measured differences in resistance gene diversity would impact infection levels, mortality rates and local abundance of tree species. Results of this study will improve understanding of plant-pathogen interactions, with potential applications for agriculture and horticulture (e.g. increasing pathogen resistance in crops). Hands-on training in cutting-edge genetic techniques would be provided to a wider audience through a summer workshop for students and faculty.This study will be the first to obtain large transcriptome datasets from a tree community and will provide gene sequence data that will be informative for future studies of genetic diversity in tropical forests. Examination of the effects of resistance gene diversity on forest dynamics will bridge the gap between molecular evolution studies that indicate ongoing selection for multiple resistance genes at many loci, and how this diversity functions in nature. Furthermore, this study is likely to bridge competing theories for tropical plant diversity by providing a genetic explanation for why rare tree species are more strongly controlled by their species-specific enemies, while simultaneously supporting dispersal limitation as a feature determining which species are locally dominant. Ultimately, the study should elucidate whether local rarity restricts local genetic diversity, which in turn reinforces local rarity, a cycle that can be escaped only by recruitment of new alleles via long-distance pollen or seed movement. Demonstrating such a coupling between the ecological and genetic features of populations would bring new perspectives and avenues for theoretical advances in evolution and ecology. The project will provide research experiences for undergraduate and graduate students, as well as a postdoctoral researcher.